Previously, there is proposed a valve device that adjusts a flow rate of EGR gas that is a portion of exhaust gas exhausted from an internal combustion engine (hereinafter referred to as an engine) (see, for example, the patent document 1).
In the valve device, a body, which receives a valve, has a receiving chamber that receives a plurality of gears, which transmit a rotational output of a motor to the valve. An opening of the receiving chamber is closed with a cover.
The cover is fixed to an end surface of a body at a plurality of fixation points in a state where a gasket, which is shaped into a ring form, is clamped between the end surface of the body and an end surface of the cover. A gasket groove, which receives the gasket, is formed at the end surface of the cover and/or the end surface of the body.
The gasket is a seal material that is made of synthetic rubber and hermetically seals between the end surface of the body and a bottom surface of the gasket groove. The gasket includes fixation segments that are clamped between the body and the cover and are respectively placed adjacent to the fixing points between the body and the cover.
The valve device limits intrusion of the water from an outside into the receiving chamber because of the presence of the gasket.
However, in a case where a distance between adjacent two of the fixing points is relatively long, specifically at a location, which is far from the fixation segments of the gasket, particularly a center segment between the fixation segments, the cover may be resiliently deformed by a resilient repulsive force that is generated through compression of the gasket in some cases. This may result in a reduction in the compression ratio at the center segment of the gasket.
Furthermore, the cover may be resiliently deformed by a pressure change in the receiving chamber under the high temperature environment. This may result in a reduction in the compression ratio at the center segment of the gasket.
Thus, at the center segment of the gasket, the hermetic sealing performance will be likely reduced in comparison to the fixation segments of the gasket. Thereby, the waterproof performance against the externally applied water (e.g., high-pressure washing water, rainwater) may be disadvantageously deteriorated.